* Sherlock: As you know, you can’t force someone to get help. They have to want it.

* Math Guy: To recap, I’ve spent the last few months of my life playing a game that was designed to kill me.

* Sherlock: A flame war does not a murderer make.

Synopsis: At the brownstone, Kitty is practicing single stick as Joan arrives. Sherlock introduces them to a skilled knife thrower. Joan asks Kitty to assist her on an investigation. Kitty, however, turns her down. The half-naked math guy is making progress. He gets dressed and heads off in search of a clue. Instead he finds a dead man. Gregson and Bell talks to him in interrogation. He tells them about a math game he’s been playing. It’s a scavenger hunt. He calls for Sherlock and Joan. The pair come to the station. The math guy gets cleared. Gregson leaves him in Sherlock and Joan’s care. They all head back to the scene. The side job Joan offered Kitty is discussed. Sherlock discovers the phone number that’s been covered up so no one else can continue the math game. Sherlock and the math guy visit one of the contestants. He determines she knows the dead man based on the dog cookie. Turns out the dead guy is her ex. Kitty gives Joan an update on the man she wanted tailed (Sherlock intervened). Joan gets a call from Sherlock with an update. Bell and Sherlock go to meet another contestant in the math game. Sherlock hears something and pushes Bell out of the way. Seconds later the contestant fires a shotgun through the door and then disappears. Copies of all the math he was working on were sent to Sherlock’s for the math guy to analyze. Sherlock and Joan work at her place and her boyfriend basically runs from Sherlock. He’s not thrilled with her relationship, but she doesn’t care. They move on to Kitty. Joan has some concerns, she thinks Kitty needs additional help. Sherlock starts talking of Kitty as if she is a child and Sherlock and Joan are her parents. Math guy’s analysis tells them that he had only solved the first 9 problems, not the 10th. However, he has figured out where the missing man went. Sherlock suspects it will actually be a murder scene and he’s right. This man is killed the same way as the first. Sherlock deduces that the killer is actually the person running the math game and that the math game is actually a trap. Back at the brownstone, Sherlock learns that the math institute is not sponsoring the game. Joan calls with a cryptic clue. He says he can identify the killer. He shows him a blog. The collection of mathletes are trying to find a signature in the math. The math guy decides to get out of town but Sherlock stops him and accuses him of being the murderer. At the brownstone, they have a lengthy conversation about his work and crimes. He leaves Sherlock confused when he calls him his friend. Later that night Sherlock and Joan video chat. Joan suggests that maybe the hunt was constructed with another hunt inside of it. Sherlock tries to get Kitty to go to a support group. She just agrees to go right out of the blue. Kitty then stands up for the math guy. Sherlock makes a disguised call outing the math guy as the one behind the blog. He then goes to meet with the math guy. He’s deduced that he was looking for one singular mathematician. He tells him about a scratcher that he hacked and then posted about it. Someone else figured out the same thing and was using it to win a lot of money. Sherlock figured out who it was, Paul, the guy at the penthouse who called all the math people together. He’s worried he’ll go to jail. But Sherlock has fixed that. Sherlock cheers him up by telling him he’s a tremendous asset. Meanwhile, Joan goes to see Kitty. She got the name of the woman in the photos. The man wanted to buy the building because it had a lost work. Kitty then tells her she’s going to a support group meeting. She tells Joan that she needs her help too. Joan goes with her to a meeting.